This invention relates to the control of microelectromechanical switches.
High speed, high precision switching devices are becoming required for a wide variety of applications. In optical communications for example, information is encoded in a modulated beam of light and transmitted via fiber optics. The encoded information is routed to the appropriate destination by a network of opto-electronic switches, which convert the light into electrical signals in order to direct the flow using standard electronic devices.
There is a need in this technology to replace opto-electronic switching mechanisms with all-optical devices. All-optical switching avoids the conversion losses and complexities associated with the transduction of the laser light into electrical signals, resulting in an overall improvement in the performance parameters of the information system.
In an all-optical switch, an optical element steers a laser beam from one of a plurality of input fibers, to one of a plurality of output fibers. The optical element may be a millimeter-sized mirror or grating, mounted on a microactuator. The microactuator may extend the element into the path of the beam to intercept it, or it may rotate the element to redirect the beam, or it may retract the element to allow the beam to pass. Arrays of optical elements may be individually mounted on corresponding arrays of microactuators, to handle Nxc3x97M fabric switches which direct light from N input fibers to M output fibers. To achieve acceptable performance, these microactuators may be required for the actuator to operate on millisecond time scales, and with micro-radian accuracy.
For optical communications as well as other applications, cost, power, speed and accuracy requirements have motivated the development of microscopic actuators using photolithographic techniques. These devices are known as microelectromechanical systems, or MEMS. Because of their small size, MEMS switches generally have high precision, low inertia and low power requirements. Batch fabrication techniques may also make MEMS a low cost approach to switching arrays.
Micromechanical switches such as those proposed for optical telecommunications generally have a member or armature driven between a plurality of mechanically stable states. That is, the system has a number of positions in which the driven member can reside in equilibrium, in the absence of a driving force. Frequently, the system is bistable, i.e. there are two positions in which the driven member can reside in equilibrium. In the example of the optical switch, the two states might be with the optical element xe2x80x9cextendedxe2x80x9d or xe2x80x9cretractedxe2x80x9d. In the case of an electrical switch the two states might be xe2x80x9coffxe2x80x9d or xe2x80x9conxe2x80x9d. In the case of a valve, the two states might be xe2x80x9copenxe2x80x9d or xe2x80x9cshutxe2x80x9d. An energy barrier, generally created by springs, cams and/or mechanical detentes, separates the equilibrium positions. The job of the actuator is to shift the driven member over the energy barrier between these states, within a prescribed switching time. An example of such a bistable magnetostatic microactuator is found in the co-pending parent application, U.S. patent application Ser. No. 09/764919, filed Jan. 17, 2001.
However the use of springs in these systems also creates the possibility of oscillation about the equilibrium position. In general, the switch is not useable until a minimum vibration or residual motion is reached. This settling time can add significant delays to the system performance. Settling time can be improved at a cost, by adding viscous or dispersive mechanisms to damp out vibration, or by adding active feedback control to the actuation device. Either choice carries a significant burden in terms of cost, complexity and power consumption. Therefore, a problem remains with micromechanical switches, in that settling time may be a primary limitation on the device performance and suitability for a given application.